The invention relates to nonwoven filter products and methods and apparatus for their manufacture. More particularly, the invention relates to methods and apparatus useful in manufacturing nonwoven filter products and nonwoven tubular filter products produced continuously thereby.
Various filter products are continuously manufactured and subsequently cut to desired sizes, shapes, and/or lengths for particular filter applications. One particular type of filter product is produced continuously in a tubular shape by depositing fibers onto a mandrel. A die is positioned adjacent the mandrel and fibers are fed through the die to contact the mandrel. Typically, the mandrel is rotated while initially deposited fibers contact the mandrel surface forming an inner diameter of the filter product. Subsequently deposited fibers form layers upon the initially deposited fibers, thereby building filter thickness radially outward to an exposed outer surface of predetermined diameter. Meanwhile, the filter product is either continuously or incrementally extracted from the mandrel to expose the mandrel surface for receiving additional fibers. In this manner, the tubular filter product is continuously produced.
Such tubular filter products have many uses. For example, in many chemical and beverage processing operations, tubular filter are used to remove particulate matter from liquids by passing the liquid around the outside of the tubular filter product while forcibly drawing the liquid from the inside of the tubular filter product. In this manner, the liquid is forced through the tubular filter, i.e., toward its inner diameter, the filter acting to trap the particulates while allowing the liquid to pass through to the open center. Of course, in other applications the process is reversed and the liquid/particulate solution is introduced in the open center of the tubular filter and forced outward through the filter to the outer diameter of the tube.
In one technique for manufacturing such filter products, the tubular body of the filter is contacted upon its outer surface by the smooth outer surface of a driven roll. The roll is driven in a direction opposite to the rotation of the mandrel such that friction between the roll outer surface and filter product causes the filter product to also rotate in a direction opposite rotation of the mandrel. In this manner, the filter product is continuously extracted from the mandrel.
In one aspect, the invention provides a method for manufacturing tubular filter products. The method includes rotating a mandrel in a first rotational direction, depositing nonwoven fibers onto the mandrel to form a tubular body, and continuously withdrawing the tubular body from the mandrel by engaging a peripheral surface of the tubular body with one or more detents extending radially from an opposed surface of a roller. The roller rotates in a direction substantially opposite the rotational direction of the mandrel as one or more detents engage the periphery of the tube to a predetermined depth.
Variations of this aspect of the invention may include one or more of the following features. The peripheral surface comprises the outer surface of a fully formed tubular body. The method further includes covering the peripheral surface with additional nonwoven fibers. The roller includes multiple detents. The multiple detents extend radially to equal distances from the surface of the roller. The multiple detents are uniformly distributed about the roller.
In another aspect, the invention provides a tubular filter product including a plurality of melt blown fibers interengaged to form a tubular body defining an outer surface and an inner surface, the tubular body further defining a pattern of cavities.
Variations of this aspect of the invention can include one or more of the following features. The cavities are enclosed between melt blown fibers of the outer surface and the inner surface. The cavities are exposed recesses extending into one of said inner and outer surfaces. Localized areas corresponding to the recesses are of greater melt blown fiber density per unit volume than an average melt blown fiber density per unit volume associated with the tubular filter product.
In another aspect, the invention-provides an apparatus for continuously producing a tubular filter product. The apparatus includes a melt blowing die assembly for expelling melt blown fibers, a rotating mandrel arranged to receive the melt blown fibers from the melt blowing die assembly for allowing the melt blown fibers to accumulate in a tubular body thereon, and a rotating roll having an outer surface with at least one detent protruding therefrom, the roll arranged so that said detent comes within a predetermined distance of the mandrel for contacting the tubular body of melt blown fibers in a manner forcing the melt blown fibers accumulated in the tubular body on the mandrel to move in a direction parallel to the mandrel.
Variations of this aspect of the invention may include one or more of the following features. The rotating mandrel extends adjacent the melt blowing die assembly to define a fiber receiving portion of the mandrel and the rotating roll is arranged to contact the tubular body at a location corresponding to the fiber receiving portion. The rotating roll has a plurality of detents protruding from its outer surface. The detents are uniformly distributed about the outer surface of the roller.
The method and apparatus provide many advantages over other techniques for manufacturing filter products. For example, great control over the filter-making process and great design flexibility for producing tubular filters having desirable characteristics because the many variables involved in the manufacturing process can be pre-selected and varied as desired. Such variables include, for example, the pre-set shortest distance between the tips of the detents and the mandrel; the outer diameter of the filter product at the point of contact with the detents, which, in turn, is dependent on the feed rate of fibers from the die, the rotational speed of the mandrel and the relative placement of the roll relative to the die; the rotational velocity and cant angle of the roll relative to the mandrel, and the rotational velocity of the mandrel. Thus, the method and apparatus provide for great control over the filter-making process and great design flexibility for producing tubular filters having desirable characteristics. Furthermore, the process of removing the filter product from the mandrel provides an easy and simple means of starting the filter making process without the need for additional equipment and starter pieces as are necessary in various known systems.
The filter products manufactured by the disclosed method and apparatus also offer many advantages over other filter products. For example, the cavities formed in the filter product provide for enhanced filtration characteristics. These cavities have been shown to provide bypass areas for fluid to pass further into the depth of the filter and provide areas for increased amounts of sediment to collect, thereby increasing the overall sediment (e.g., dirt) holding capacity of the filter proportionally by the number, size and shape of the cavities created during processing. Additionally, the penetration of detents into filter product locally compresses the affected fibers against one another. This compressing action increases the overall collapse strength of the filter product by interlocking the affected fibers of the various layers penetrated by the detents as well as closely adjacent fibers.